A multi-speed bicycle on the market is equipped with a drivetrain as shown in FIG. 1. Refer to FIG. 1, which is a schematic top view of a drivetrain 100 of a conventional multi-speed bicycle. The drivetrain 100 in FIG. 1 belongs to a 1X transmission system and includes a drive chain 110, a freewheel 120 and a chainwheel 130. The chainwheel 130 is a single chainring and is connected with a crank (not shown). The freewheel 120 has a plurality of sprockets 121 stacked on each other and is connected to a rearwheel (not shown).
The sizes of the sprockets 121 are different from each other. As seen in FIG. 1, the sprockets 121 are arranged from top to bottom in an order from large to small, so the uppermost sprocket 121 in FIG. 1 has the largest diameter, whereas the lowermost sprocket 121 in FIG. 1 has the smallest diameter. The drive chain 110 engages with the freewheel 120 and the chainwheel 130 and has flexibility, so that the drive chain 110 can be bent in the direction of a rotational axis A12 of the freewheel 120 and a rotational axis A13 of the chainwheel 130. Thus, the drive chain 110 can be selectively engaged with one of the sprockets 121 to achieve a multi-speed function.
However, the drive chain 110 is bent in the directions of both the rotational axis A12 and the rotational axis A13 so as to generate a lateral stress which can causes friction between the drive chain 110 and both of the freewheel 120 and the chain wheel 130. The greater magnitude of the drive chain 110 is bent (in the direction of the rotation axes A12 and A13), the greater the lateral stress would be, so that the greater friction could be generated. Once the friction is greater than a certain degree, not only a louder noise is generated when riding the bicycle, but also the drive chain 110, the freewheel 120, and the chainwheel 130 would be worn out quickly. Even the risk of disengagement of the drive chains 110 with the freewheel 120 or the chainwheel 130 may be increased.
The section of BACKGROUND OF THE INVENTION is used merely to aid in the understanding of the present disclosure, and what is disclosed in BACKGROUND OF THE INVENTION may include some of the conventional techniques that are not known to those of ordinary skill in the art. Moreover, what is disclosed in BACKGROUND OF THE INVENTION does not imply that the content or the problem to be solved by one or more embodiments of the present disclosure and does not mean that it has been known to those of ordinary skill in the art before the application of the present disclosure.